Don't let other people make or break your self-image

That wisdom is just as important once you're in a relationship. PM_ME_YOUR_PARTYPICS writes: "Don't go into a relationship expecting to be made happy. You have to be able to be happy on your own first."

Love isn't enough for a solid relationship

"Just because you love each other does not mean that you're good together long-term," writes abqkat. "I love pizza, I loved my high school sweetheart - both make my stomach feel bad and I should have no part in either."

"The problem is that love isn't enough. You both have to be committed. There may be times you don't feel like you love each other, like you're so hurt or angry that you can't stand the sight of the other.

"But if you're both committed to the relationship, to the promises you made, then you'll work through it and you'll become stronger. Love without commitment just isn't enough."

Focus on your own relationship — not your friend's

"Practically everyone has a relationship that looks perfect from the outside looking in," writes BrawndoTTM. "Unless you are EXTREMELY intimate with your friends, you will never have any idea what that couple's actual problems are until they break up and spill the beans."

Indeed, research suggests that people are notoriously poor judges of what others are thinking and feeling. That finding may extend to relationships — if you assume your friend and her husband are completely happy in their marriage, you're probably wrong.

4/

'The Break-up'/Universal Studios

Conflict is inevitable

Dummystupid says: "No relationship is perfect and there will be conflict. What matters is the desire to solve the problem."

And bamber79 writes: "When you and your SO are arguing, remember- it's you and them VS the problem. Not you VS them. This has helped me tremendously in how I approach disagreements."

John Gottman, a psychologist and cofounder of the Gottman Institute, previously told Business Insider that the No. 1 commonality in successful relationships is the ability to repair the partnership after a conflict. In other words, conflict itself isn't the problem.

"In really good relationships, people are very gentle with the way they come on about a conflict," Gottman told Business Insider. "They don't bare their fangs and leap in there; they're very considered."

You need to work to keep the spark alive

"Once you're in a long-term relationship/marriage, never stop dating your SO," writes BandofDonkeys. "There needs to be some sort of constant courtship to make them feel you still want them, even after all these months/years."

Research supports this Redditor's observation: A 2012 study from the University of Kentucky and West Virginia University found that "flirting" is important for married couples, too. Of the 164 couples the researchers studied, most flirted — by playing "footsies" or whispering in their partner's ear, for example — in order to maintain intimacy.